It depends if you are able to replicate the results obtained earlier using the cheaper polymerase.

If you can't, then yes you will need to optimise all the parameters again.

Keep in mind that it is not a guarantee you will be able to replicate it though. While I haven't had any problems using a cheaper polymerase, some of my friends found that their template or intended region can only be obtained using more expensive polymerases. So it might not end up as the most "cost-effective" option if you spend all the time re-optimising the parameters but are still unable to replicate the results.

[Only registered users see links. ] The concentration of each primer should be between 0.1 and 0.5 mM. For most applications 0.2 mM produces satisfactory results. Too high primer concentrations increase the chance of mispriming, which results in nonspecific PCR products. Limiting primer concentrations result in extremely inefficient PCR reactions.